Municipal wastewater treatment plants play a critical role in protecting human health and the environment, but the operation of such plants consumes an extensive amount of energy and the management of nutrients (e.g., nitrogen and phosphorus) remains a challenge. For instance, it has been estimated that approximately 3-5% of electricity consumed in the United States is consumed by water treatment and wastewater management infrastructure. As such, an ongoing challenge is the development of improved wastewater management with reduced energy demands and nutrient recovery.
A variety of technologies have been employed to produce fresh water from wastewater. One such technology is a microbial fuel cell (MFC) in which electricity may be harvested directly during microbial metabolism of organic matter. Specifically, in a MFC, organic matter (e.g., organic contaminants in wastewater) is metabolized by microbes in an anode chamber thus transferring electrons to the anode and liberating protons into the aqueous phase such that the electrons flow through a wire from the anode to a cathode to produce an electrical current. At the cathode, the electrons are accepted by a terminal electron acceptor (e.g., oxygen). Additionally, ion transport between the anode and cathode is needed to maintain proper change balance in the microbial fuel cell and to facilitate the generation of electricity. A microbial fuel cell, while removing organic contaminants from wastewater, does not remove other contaminants (e.g., salts, heavy metals, etc.) and thus further treatment is required to obtain fresh water.
A second such technology is algal bioreactors in which algae uptake nutrients such as nitrogen and phosphorus from water to support algal growth and fix carbon dioxide via photosynthesis to produce biomass and oxygen. Algal biomass may be converted into biofuels, e.g., biodiesel. Algal bioreactors, however, do not remove other contaminants (e.g., organic contaminants, heavy metals, etc.) from wastewater and thus further treatment is required to obtain fresh water.